The present invention relates to a tactile switch unit and, more particularly, to a tactile switch unit which has a plurality of press areas corresponding to a plurality of switches and possesses an illuminating function.
FIGS. 1A, 1B and 1C schematically show the general configuration of a conventional switch unit of this kind disclosed in Japanese Patent Application Publication Gazette No. 8-315682. The illustrated prior art example has three press areas.
A keytop 1 is adapted to turn about a pivot shaft 1a extending along one end thereof. On the keytop 1 there is mounted a membrane sheet 2, on which is laminated a surface sheet 3.
The surface sheet 3 has a row of three press areas 3a each including a symbol 3b as depicted in FIG. 1A.
In the membrane sheet 2 there is formed right under each press area 3a a membrane switch 2a composed of a pair of opposed contacts. In FIG. 1B reference numerals 2b, 2c and 2d denote a top sheet, a bottom sheet and a spacer which constitute the membrane sheet 2.
Under the keytop 1 there is disposed a base plate 4, on which there are mounted light sources 5 and a xe2x80x9cclickxe2x80x9d tactile push-button switch 6. In this example, three light sources 5 are provided each corresponding to one of symbols 3b, and the push-button switch 6 is located on the side opposite to the pivot shaft 1a of the keytop 1 and is held in abutment against the underside of the keytop 1.
In the unit switch of such a construction as mentioned above, when a desired one of the press areas 3a is pressed, the both contacts of the membrane switch 2a right under the pressed area 3a get into contact with each other as shown in FIG. 1C, by which the membrane switch 2a is turned ON and the pressed area 3a is detected preliminarily, then further pressing of the press area 3a turns the keytop 1 about the pivot shaft 1a to urge the push-button switch 6 into the ON state, and as a result, the pressed area 3a is detected ultimately.
Each symbol 3b is illuminated by light emitted from the corresponding light source 5 and transmitted through the keytop 1 so that the symbol 3b can be visually recognized even in the dark, for instance.
Incidentally, in the switch unit of the above construction, the pair of opposed contacts making up the membrane switch 2a is usually formed by print-coating a carbon paste or similar conductive paste on the top and bottom sheets 2b and 2c; that is, the membrane switch 2a is formed of a material which inhibits the passage therethrough of light.
Accordingly, the light emitted from the light source 5 mounted on the base plate 5 for illuminating the symbol 3b is cut off by the membrane switch 2a located right under the pressed area 3a, casting the shadow 3c of the membrane switch 2a onto the symbol 3b and hence preventing the symbol from being illuminated with a uniform brightness.
Since the surface sheet 3 and the membrane sheet 2 are held in close contact, the above phenomenon occurs inevitably no matter where the light source 5 is located. Accordingly, the conventional switch unit of FIGS. 1A, 1B and 1C is incapable of illuminating every symbol 3b with a uniform brightness.
On the other hand, in the case where two columns of press areas 3a are arranged in parallel to a pivot axis 1b of the keytop 1 as depicted in FIGS. 2A and 2B, the tactile feedback differs when the press areas 3a of the first column next to the pivot axis 1b are pressed and when the press areas 3a of the second column away from the pivot axis 1b are pressed.
FIGS. 3A and 3B show the state of the press areas 3a of the first and second columns being pressed, respectively. The difference in tactile feedback is attributable to the difference between the distances from the pivot axis 1b to the press areas 3a of the first and second columns; such nonuniform tactile feel is unwanted in terms of quality.
To provide uniform tactile feedback, the press areas 3a need to be aligned in parallel to the pivot axis 1b; in other words, uniformalization of tactile response does not allow free arrangement of the press areas, and hence imposes severe limitations on their arrangement.
Moreover, in the conventional switch unit the membrane sheet 2 and the surface sheet 3 are bonded together on the keytop 1, and in order to facilitate this bonding, the membrane sheet 2 and the surface sheet 3 are made smaller in outside shape than a concavity 1c of the keytop 1 for receiving them as shown in FIGS. 4A and 4B.
Accordingly, looking from the operating panel side of the switch unit, a clearance 7 is just visible between the marginal edge of the surface sheet 3 on all sides and the keytop 1xe2x80x94this impairs the appearance of the switch unit. Reference numeral 8 in FIGS. 4A and 4B denotes a case.
As a solution to this problem, it is possible to use such a structure as shown in FIGS. 5A and 5B, in which the surface sheet 3 is larger in outside shape than the concavity 1c of the keytop 1 and has its marginal portion downturned on all sides as indicated by 3d to completely cover the keytop 1.
In this instance, however, it is necessary to bond the surface sheet 3 to the membrane sheet 2 while bending the marginal portion of the former on all sides substantially at right angles theretoxe2x80x94this leads to difficulties in bonding the surface sheet 3 to the membrane sheet 2 in close contact therewith and in positioning the surface sheet 3.
Furthermore, in the conventional switch unit having the surface sheet 3 and the membrane sheet 2 bonded together in close contact with each other, when the top surface of the surface sheet 3 containing the symbols 3b is formed three-dimensional, curved or uneven, the surface of the keytop 1 which directly receives the membrane sheet 2 also needs to be formed in the same configuration as that of the surface sheet 3, but since it is extremely difficult to conform the membrane sheet 2 to the surface configuration of the keytop 1, it is practically impossible to make the top surface of the surface sheet 3 three-dimensional, curved or uneven.
It is therefore an object of the present invention to provide a tactile switch unit which: enables every symbol to be illuminated over the entire area thereof with uniform brightness; provides constant tactile response no matter which of arbitrarily arranged press areas is depressed; has an enhanced appearance; and permits easy implementation of the desired three-dimensional or similar surface configuration of the surface sheet.
According to the present invention, there is provided a tactile switch unit which comprises:
a case;
a link mechanism having first and second link members disposed in said case, rotatably supported intermediately of their ends to said case and having their inner ends rotatably coupled to each other;
a slider located above said link mechanism and vertically movably housed in said case, and having a flat top and a plurality of legs for rotatably supporting outer ends of said first and second links;
a membrane sheet disposed on said flat top of said slider and having formed therein a plurality of membrane switches;
a knob fixedly integrated with said slider and having apertures in its top panel fitted in a top opening of said case;
a surface sheet having formed thereon a plurality of press areas and disposed on the top panel of said knob with said press areas aligned with said apertures;
a pusher having a plurality of pusher elements disposed on said membrane sheet in opposing relation to the back of said press areas, respectively, each of said pusher elements being designed so that upon depression of said press area corresponding thereto, said each pusher element is pressed to urge said membrane switch corresponding thereto;
a tactile push-button switch disposed in said case and turned ON/OFF by pivotal movement of said link mechanism;
a bottom plate attached to said case on the bottom side thereof; and
a light source mounted on the inside surface of said bottom plate, for illuminating a symbol provided in said each press area;
wherein said membrane sheet except a conductor portion and said pusher are formed of a light transmitting material.
In the above switch unit, at least one of the link mechanism and the slider may have a hole formed therethrough to pass light from the light source to each symbol.
In the above switch unit, the link mechanism may be provided with a third link member rotatably supported by either one of the first and second link members so that the push-button switch is turned ON/OFF by the third link member.
The above switch unit may be provided with storage means which stores ON information about the membrane switch turned ON by depression of the corresponding press area and from which the stored ON information is output upon turning ON of the push-button switch.
The above switch unit may have a construction in which each of said pusher elements has a cylindrical configuration with one end closed and is disposed with said closed end face opposite the back of said press area corresponding thereto, a protrusion for pushing said membrane switch being provided on the open end portion of said each pusher member at one side thereof and said open end portion being supported by a hinge on the side opposite from said protrusion.
In the above switch unit, the knob may be a molding with the surface sheet inserted therein.